The perennial plant Convolvulus arvensis, better known as field bindweed or wild morning glory, is a serious agricultural problem around the world with the exception of the tropics. Field bindweed infestations are encountered along roadsides, in city green spaces and cultivated lands throughout most of the U.S. and Canada and it has been classified as one of the most important weeds worldwide.
Phenoxy herbicides such as (2,4-dichlorophenoxy)acetic acid (2,4-D), (4-chloro-2-methylphenoxy)acetic acid (MCPA) and 3,6-dichloro-2-methoxybenzoic acid (DICAMBA) are presently used for the control of this pest. Although, these compounds are among the most effective and commonly used herbicides they are generally costly and ineffective in suppressing the spreading of bindweed. For example, in California, field bindweed is more prevalent now than 20 years ago in spite of the intensive control programs used.
In the early 1970's, a number of independent studies on the biological control of field bindweed were initiated.
Among them, insects and gall mites were considered but were found to be inadequately host-specific causing damage to crop plants in addition to the weeds.
Fungi which are pathogenic to field bindweed present an alternate possibility for its biological control. Phomopsis convolvulus, an organism which was isolated and identified recently by Ormeno-Nunez et al (Plant Dis., 1988, 72, 338 and Can. J. Bot. ,1988, 66, 2228) is one such pathogen. The Phomopsis convolvulus has been deposited in The Commonwealth Mycological Institute in Kew, England and assigned the accession number IMI 303662. It has been shown to infect field bindweed causing brown lesions which sometimes are surrounded by yellow haloes characteristic of phytotoxin production.
In general, the genus Phomopsis includes several pathogenic fungi which cause a variety of disease symptoms to plants, animals and occasionally humans. The majority of these microorganisms have not yet been thoroughly investigated and only a few are known to produce biologically active metabolites. Among these metabolites are the cytochalasins, which are mammalian toxins exhibiting a number of unusual effects on animal cells, sometimes plant cells, and on microbial cells. Other biologically active metabolites from Phomopsis fungi include the ionophoric mycotoxin phomopsin A isolated from Phomopsis leptostromi and several insect deterrent metabolites of Phomopsis oblonga.
However, a herbicidal metabolite effective against field bindweed has never been isolated before from a Phomopsis fungus or any other source. In addition, since Phomopsis convolvulus is a host-specific pathogen of field bindweed it would be highly desirable if any metabolite responsible for its pathogenicity on this agricultural pest produced therefrom, could be isolated and identified.